1. Field of the Invention
The present invention relates to an on-vehicle distribution box and a distribution system utilizing the distribution box for distributing an electrical power to a first load operated on a first voltage and to a second load operated on a second voltage differed from the first voltage.
2. Related Art
An automobile vehicle has a battery supplying an electrical power to an engine starting system including a cell motor and an ignitor and to other systems including in-cabin indication meters and electrical equipment Generally, the battery is 12 V in ordinal passenger cars and 24 V in larger-size vehicles like a truck and a bus.
However, some loads of the vehicles may not operate efficiently on such voltages and may require a power having a voltage higher than 12 V (volts) or 24 V (volts).
To fulfill such requirement, there has been proposed an automobile power source circuit disclosed in Japanese Patent Application Laid-open No. H. 5-155296. The circuit can apply 24 V voltage by connecting two 12 V batteries in series at a starting condition and can apply 12 V voltage by using the two 12 V batteries in parallel during a normal operation of the automobile.
However, the above-mentioned automobile circuit has not sufficiently satisfied the need of providing a higher voltage even during a normal operating condition to loads other than the starting system.
Furthermore, as another proposal, Japanese Patent Application Laid-open No. 9-169217 discloses a DC/DC converter unit, in which a high voltage circuit connected to a high voltage battery is branched at a position downstream from a main fuse. The branch circuit is connected to a converter via a secondary fuse to convert the high voltage into a lower voltage for supplying an electrical power to low-voltage loads like lighting equipment.
Nevertheless, the above-mentioned DC/DC converter unit provides a higher voltage circuit in all the upstream side of the DC/DC converter, so that the secondary fuse must has the same high voltage constitution as the main fuse, causing an increased cost of the fuse. Furthermore, the secondary fuse for the high voltage is not satisfactory for protecting low-voltage equipment arranged downstream from the converter in the event of an excessive current, which may cause a damage in the low-voltage equipment.
In view of the above-described circumstances, an object of the invention is to provide an on-vehicle distribution box and an on-vehicle distribution system which efficiently provide a power source having both a first voltage suitable for relatively higher voltage loads and a second voltage suitable for relatively lower voltage loads, surely preventing the damage of the loads in the event of an overcurrent.
For achieving the object, first and second aspects of the present invention relate to an on-vehicle distribution box, and a third aspect of the present invention relates to an on-vehicle distribution system.
The first aspect is an on-vehicle distribution box for distributing an electrical power supplied from a power source to a first voltage load operated on a first voltage and a second voltage load operated on a second voltage differed from the first voltage. The distribution box includes:
a primary circuit of which an upstream point is connected to the power source and of which a downstream point is connected to the first load,
a first fuse means provided in the primary circuit,
a branch circuit branched upstream from the first fuse means from the primary circuit and connected to the second load at a downstream point of the branch circuit,
a DC/DC converter arranged in the branch circuit for converting the first voltage to the second voltage, and
a second fuse means arranged in the branch circuit downstream from the DC/DC converter.
The second aspect is the distribution box described in the aspect 1, wherein the first voltage is higher than the second voltage.
The third aspect is an on-vehicle distribution system comprising a main distribution box and a secondary distribution box each of which has the constitution of the distribution box described in the aspect 1 or 2, wherein an upstream point of the secondary distribution box is electrically connected to a downstream point of the primarily distribution box.
Next, operational effects and advantages of the present invention will be discussed.
In the first aspect, the distribution box has the second fuse means provided between the second load and the DC/DC converter in the branch circuit. The second fuse means may have a shutdown character adequately set for the second voltage operating the second load.
Thus, with no restriction imposed by the electrical load condition of the vehicle, the first and second voltages different from each other are supplied efficiently respectively to each first or second voltage load, surely preventing a damage of the first and second loads in the event of an overcurrent.
In the second aspect, the distribution box provides a high voltage circuit for supplying an electrical power directly supplied from the battery to the first load before converting it by the DC/DC converter.
Thus, the maximized amount of the high-voltage circuit of the vehicle reduces a transmission loss of the electrical power.
The third aspect provides an on-vehicle distribution system having the secondary distribution box connected to a downstream point of the main distribution box and constituted basically in the same way as the main distribution box. The main and secondary distribution boxes have the primary and branch circuits for distributing the electrical power to the first and second loads, which provides a decentralized power supply system.
The first and second voltage loads each are connected to a downstream side of the primary circuit or the branch circuit of the main or secondary distribution box. Particularly, each of the second voltage loads operated on the second voltage differing from the battery voltage receives an electrical power through one of the DC/DC converters. That is, the voltage conversion is distributively carried out by the DC/DC converters of the distribution boxes. Thus, a heat radiation generated during the voltage conversion is divided for the DC/DC converters to prevent a centerized large amount of heat radiation, thereby eliminating an additional structure for heat radiation or for cooling. This reduces the DC/DC converters in size, allowing an easy installation of them in the distribution boxes. As a result, the distribution boxes are also decreased in dimension, which is advantageous when mounted in the vehicle.
Moreover, in an accidental event of one of the second voltage loads, which is arranged downstream from one of the DC/DC convector, an electrical power supplied to the second voltage load may be shut off by stopping the operation of the related distribution box without interrupting all the electrical power supply.